Oil is used as a lubricant and coolant for the components in an axle or axle tube. This coolant prevents over-heating and operates to increase the life of the components within the axle. But using a coolant that is in intimate contact with the components in the axle causes some challenges for service-ability. One challenge for service-ability is the fact that at least some of the oil must be drained to access the internal components. Moreover, the internal components must be compatible with the coolant and be able to be soaked in the coolant without the coolant causing significant degradation. Further, electrical connections within the axle become bathed in oil and impart difficulty (i.e., oily and slippery) in maintaining and changing worn connections.
Additionally, mechanical contact of internal axle components to the axle frame across multiple points inherently transfers some vehicle load through the bearings and rotating components. As a result, this transfer of vehicle load necessitates that using more expensive bearings or shorter longevity of lesser expensive bearings.
Because of this mechanical contact to separate and keep oil out of certain axle areas is undesirable should it lead to load transfer into bearings as this will lead to more expensive bearings and/or shorter life of bearings.